1. Field of the Invention
The present invention relates to a communication apparatus and a communication system, and more particularly, it relates to a communication apparatus connected to a local area network and a communication system constituting a local area network.
2. Description of the Background Art
A communication apparatus connected to a local area network, a communication system constituting a local area network or the like is known in general. Such a communication apparatus is disclosed in each of Japanese Patent Laying-Open Nos. 2008-11081, 2005-268888, 2004-48260, 2002-77262 and 11-27310, for example.
The aforementioned Japanese Patent Laying-Open No. 2008-11081 discloses a communication apparatus connected as a terminal of a local area network (LAN) and capable of communicating with an external network through a gateway router. In this communication apparatus described in Japanese Patent Laying-Open No. 2008-11081, when a plurality of communication apparatuses constituting the LAN transmit/receive packet data to/from a communication apparatus connected to other LAN through the external network, each communication apparatus performs address learning for an IP address which reception packet data has (processing for storing the IP address of each communication apparatus constituting the LAN), thereby specifying a destination communication apparatus.
The aforementioned Japanese Patent Laying-Open No. 2005-268888 discloses a communication apparatus controlling a LAN connected with a plurality of terminals and controlling data communication with other LAN or a wide area communication network (WAN). In the communication apparatus described in the Japanese Patent Laying-Open No. 2005-268888, when the plurality of terminals constituting the LAN transmit/receive packet data to/from a terminal connected to other LAN through the external network such as the WAN, each terminal performs address learning for an IP address (corresponding to Ipv6) which reception packet data has (operation for storing IP address of each terminal), thereby specifying a destination terminal.
The aforementioned Japanese Patent Laying-Open No. 2004-48260 discloses a packet transfer method and a packet transfer system for use in connecting a mobile terminal (mobile PC, etc.) previously connected to a prescribed LAN to other LAN in a network environment where a plurality of LANs are connected to an external network such as an Internet. In the packet transfer method described in Japanese Patent Laying-Open No. 2004-48260, a communication controller connected to a LAN controls both of IP addresses and MAC addresses (physical addresses unique to terminals) of a plurality of the mobile terminals in the LAN. Thus, when the mobile terminal is moved from the single LAN to other LAN to be connected, the communication controller is enabled to transfer packet data to a destination terminal on the basis of a substitution MAC address assigned for convenience after movement from an original MAC address.
The aforementioned Japanese Patent Laying-Open No. 2002-77262 discloses an information relay apparatus controlling a LAN connected with a plurality of terminals and controlling communication with other LAN or a WAN. In the information relay apparatus described in Japanese Patent Laying-Open No. 2002-77262, when the plurality of terminals constituting the LAN transmit/receive packet data to/from a terminal connected to other through an external network such as the LAN or the WAN, each terminal performs address learning for an IP address (corresponding to Ipv6) which reception packet data has (operation for storing IP address of each terminal), thereby specifying a destination terminal.
The aforementioned Japanese Patent Laying-Open No. 11-27310 discloses a high-speed LAN switching control method in a network environment where a plurality of LANs are connected to a single LAN switch (packet switching apparatus) and the system. In the high-speed LAN switching control method and the system described in Japanese Patent Laying-Open No. 11-27310, the system controls both of IP addresses and global MAC addresses of the plurality of terminals connected to the LAN with a control table stored in the LAN switch. At this time, the control table stores local MAC addresses (addresses assigned for convenience for distinguishing the terminals in the LAN each LAN) in addition to the aforementioned IP addresses and global MAC addresses. Thus, when communication performs between terminals, the LAN switch receiving communication request searches a destination terminal on the basis of correspondence relationship between the global MAC addresses and the local MAC addresses registered in the control table.
In the conventional communication apparatus or packet transfer method disclosed in each of the aforementioned Japanese Patent Laying-Open Nos. 2008-11081, 2005-268888, 2004-48260 and 2002-77262, however, the apparatus conceivably sequentially checks a destination address given to the packet data and the addresses in a control table to specify a destination (destination terminal) of the packet data in packet communication while controlling the IP addresses and the MAC addresses, which the terminals constituting the LAN have, with the single control table in an integrated manner. The IP addresses have 32-bit wide (in a case of Ipv4) or 128-bit wide (in a case of Ipv6), and the MAC addresses have 48-bit wide, and hence addresses having enormous quantities of data volume (bit length) must be conceivably checked for the one destination address when checking the addresses for all data. Thus, arithmetic processing in checking the addresses becomes disadvantageously considerably overloaded.
In the aforementioned conventional high-speed LAN switching control method disclosed in Japanese Patent Laying-Open No. 11-27310, arithmetic processing specifying the destination of the packet data is performed with reference to the local MAC addresses (address given for convenience for distinguishing each terminal in the LAN) in addition to the IP addresses and global MAC addresses of the terminals in packet communication, and hence the arithmetic processing becomes disadvantageously considerably overloaded due to increased reference data volume (bit length) constituted by the IP addresses, the global MAC addresses, the local MAC addresses and the like.